During the last 5 years, the adenosine A2A receptor (A2AR) has emerged as a leading non-dopaminergic therapeutic target in Parkinson's disease (PD). This excitement came primarily from two lines of experimental and clinical investigations showing multiple potential benefits of A2AR antagonists in PD (i.e. confirmed motor stimulation, potential of neuroprotection and possible anti-dyskinesia). However, major knowledge gaps need to be addressed: the molecular mechanisms for the A2AR antagonist monotherapy versus the A2AR antagonist combined therapy with L- DOPA, and for possible anti-dyskinesic as well as neuroprotective effect of A2AR antagonists. Most importantly, are the multiple benefits by A2AR antagonists mediated by a common mechanism or distinct cellular actions? The overall goal of this proposal is to dissect out the cellular basis for the multiple functions of A2AR antagonists (i.e. motor stimulation, possible anti-dyskinesic effect and potential neuroprotection) in animal models of PD. The core hypothesis of the proposal is that the distinct anti-PD properties of A2AR antagonists are mediated by A2ARs in different cellular elements. Specifically, A2AR antagonists act at post-synaptic striatopallidal neurons, presynaptic cortico-striatal glutamatergic terminals and microglia to exert motor stimulant, anti-dyskinesic and neuroprotective effects, respectively. Our three KO models with cell-type specific inactivation of the A2AR in striatal neurons, forebrain neurons, or microglial cells will allow us to investigate this hypothesis. Beyond providing basic neurobiological insights on the integrated function of A2ARs in brain, the dissection of potential distinct cellular mechanisms of A2AR antagonists opens up new and real possibilities of selectively manipulating A2AR's motor, anti-dyskinesic and neuroprotective effects by targeting different cellular elements (striatopallidal, cerebral cortical neurons, and microglia). The results of the proposed research will provide a cellular basis for the better clinical use of A2AR antagonists in PD patients. PUBLIC HEALTH RELEVANCE This proposal represents a major translational research effort to elucidate the cellular basis for the multiple functions of adenosine A2A receptors in Parkinson's disease using a series of novel cell-type specific A2A receptor knockout mouse models in conjunction with selective A2A receptor antagonists. If we identify distinct cellular populations responsible for the various actions of A2A receptor antagonists, it will open up new possibilities for selectively manipulating A2AR effects by targeting different cellular elements (e.g. striatopallidal, cerebral cortical neurons, microglial). These results will provide a cellular basis for improved clinical use of A2AR antagonists in Parkinson's disease patients.